The present invention relates to the field of nuclear power reactors which are generally of the pressurized water type. Such nuclear power reactors typically have a plurality of individual elongated and generally vertical fuel bundle assemblies which comprise the reactor core. During refueling of such a reactor core, it is typical to replace one-quarter to one-third of the total number of fuel bundle assemblies at a given time. Typically, such re-fueling of a reactor core is carried out by removing the spent fuel bundles that are to be withdrawn from the reactor core and thereafter repositioning some of the existing fuel bundles to new locations within the core and finally inserting the new fuel bundles into their desired initial position. Typically, such fuel repositioning and management is effected while the reactor core fuel assemblies are sumberged in the cooling fluid within the reactor vessel and various means for accomplishing such repositioning are employed at the top of the reactor vessel. Such means may take the shape of a traveling crane mechanism such as shown in U.S. Pat. No. 3,603,634 or U.S. Pat. No. 4,385,028.
In any event, occasionally some difficulty will be experienced in inserting a fuel bundle assembly into certain reactor core locations due to inadequate physical space to receive the fuel assembly being inserted. This space problem is generally due to a slight elastic bowing in one of the fuel assemblies bordering the core location being loaded. In some cases, the resulting rectangular opening is too small to readily receive the lower end of the fuel bundle assembly being inserted, in spite of there being small chamfers on the lower bottom tie plate of the fuel bundle assembly. When such is the case, a delay of one to two hours is typical to overcome such a problem over the time otherwise required to insert a fuel bundle wherein the empty core position is of the proper dimension to receive the fuel assembly being inserted. Such unnecessary time delay in carrying out the loading and reshuffling of position of the fuel bundle assemblies in the reactor core results in unnecessary out-of-service time for the utility reactor and delay in its subsequent startup. Such delay is at considerable economic cost to the operating utility, since it unnecessarily increases the out-of-service time of the generating facility.
The problem of physical interference upon insertion of a fuel bundle assembly into a reactor core has been addressed in typical prior art patents, such as the aforementioned U.S. Pat. No. 3,603,634. In this patent, the fuel bundle assembly being inserted is lowered down through a tubular centering device which includes a plurality of enlarged lower edge portions which are adapted to physically displace the fuel bundles adjacent the core position being loaded away from the empty core position. While the solution presented by this prior art patent may be applicable to fuel loading operations where the fuel assembly is lowered down through a centering mast or device, it is unsuitable for the environment of applicant's invention wherein a fuel bundle is merely lowered directly into an empty core position.